1. Field of the Invention
The present invention relates to an electron beam lithography method, for drawing and exposing elements that constitute an uneven transfer pattern on a master carrier for magnetic transfer, by irradiating an electron beam on a resist provided on a disk.
2. Description of the Related Art
A magnetic transfer method is known. In the magnetic transfer method, a master carrier for magnetic transfer that bears transfer data, formed by a fine uneven pattern of magnetic material, is placed in close contact with a slave medium, which has a magnetic recording portion. A transfer magnetic field is applied to the master carrier and the slave medium while they are in close contact with each other. Thereby, a magnetic pattern that corresponds to the data borne by the master carrier (servo signals, for example) is transferred and recorded on the slave medium.
As a method to produce master carriers, which are utilized in magnetic transfer, an application of an optical disk stamper production method is being considered (refer to Japanese Unexamined Patent Publication No. 2001-256644, for example). The optical disk stamper production method uses an original disk, having an uneven pattern formed of resist that corresponds to data to be transferred, as a base.
During production of the optical disk stamper, a disk (a glass plate, for example) having resist coated thereon is rotated. Data is converted to lengths of pits, and data is written into the resist by emitting laser beams, which are modulated according to the lengths of pits, onto the resist.
It is considered that drawing of the fine patterns onto master carriers for magnetic transfer may also be performed by rotating a disk having resist coated thereon and emitting a laser beam modulated according to data to be transferred, similar to the production method for the optical disk stamper.
However, miniaturization and increase of data capacity are desired in magnetic disk media. If bit lengths or track widths are decreased to accommodate increases in recording density (for example, if bit lengths or track widths become 0.3 μm or less), the decreased sizes approach the drawing limits of laser beams. Therefore, the shapes of the ends of drawn portions become arcuate, causing difficulty in forming rectangular elements of the uneven patterns. The shapes of the elements that constitute the uneven patterns of master carriers, and particularly the shapes of the upper surfaces of the elements, are those of the drawn portions. Therefore, if the ends of the drawn portions are arcuate, the upper surfaces of the protrusions of the uneven patterns on the master carrier substrate become shapes different from rectangles, such as ovals. In these cases, it becomes difficult to form desired magnetic patterns on slave media.
Meanwhile, in the field of semiconductors, patterning is already being performed by utilizing electron beams, which are capable of exposure with smaller diameter spots than laser beams. By utilizing the electron beams, it is becoming possible to perform highly accurate patterning of fine patterns.
In addition, patterned exposure using electron beams has been proposed in Japanese Unexamined Patent Publication No. 2001-110050. The patterned exposure using electron beams has been proposed to produce miniature, light weight and high recording density magnetic patterned media, the realization of which is being anticipated.
Magnetic transfer has a conspicuous advantage over conventional servo track writers when recording servo patterns that correspond to servo signal as transfer patterns. Conventional servo track writers require a long amount of time to record servo patterns in each sector of circumferential tracks using magnetic heads. In contrast, magnetic transfer is capable of simultaneously recording the servo patterns across the entire surface of a disk in a short amount of time.
However, servo signals include, for example: synchronization signals (preambles) which are recorded across the entire width of a track; address signals (gray code) such as track numbers; and burst signals for positioning heads, which are recorded across half of the width of a track. In addition, the address signals are not limited to single unit signals (1 bit signals), but include multiple unit signals (multiple bit signals). Similarly, a transfer pattern (uneven pattern formed on magnetic material), to be formed on a master carrier for magnetic transfer in order to transfer and record the servo signals, comprises elements which are of lengths that are of a reference value, corresponding to a single bit, and integer multiples of the reference value, corresponding to multiple bits. It is necessary to efficiently and accurately draw the elements, which are of varying lengths in the circumferential direction, in a resist layer provided on a disk, using an electron beam.
In addition, it is necessary for concentric patterning to be performed to produce the master carriers for magnetic transfer. Therefore, favorable pattern formation is difficult, in the case that an electron beam lithography method that employs an XY stage, as in the field of semiconductors, is adopted. Accordingly, an electron beam lithography method, which is capable of drawing patterns favorable for master carriers, is desired. Accompanying increases in the numbers of tracks (numbers of sectors), the number of elements also becomes enormous. Thus, reductions in drawing times, by improvements in drawing speeds, as well as improvements in the shapes and positional accuracy of drawn elements across the entire surfaces of disks, are desired.
Particularly in the case that the elements are drawn employing lithography, elements are drawn by rotating a disk and deflecting an electron beam in the radial and circumferential directions thereof, for a single circumferential track. However, if lithography is performed in a single radial direction, time is required to return the electron beam in the radial direction opposite the drawing direction, after deflecting the electron beam in the radial direction to draw a single unit of a multiple bit element. During this time, lithography is not possible, thereby creating blank periods between lithography of a first unit and lithography of a next unit. Accordingly, there is a problem that continuous elements, which are long in the circumferential direction, cannot be drawn. Drawing a single track during multiple rotations of the disk reduces drawing efficiency, and also causes difficulties in securing positional accuracy for drawn elements.